High-frequency wide band coupling transformer



Oct. 9, 1951 --N E. DAVIS HIGH-FREQUENCY WIDE BAND COUPLING TRANSFORMER 3 Sheets-Sheet 1 Filed April 11, 1947 INVENTOR ORNEY Oct. 9, 1951 DAVls 2,570,650

HIGH-FREQUENCY WIDE BAND COUPLING TRANSFORMER Filed April 11, 1947 3 Sheets-Sheet 2 Oct. 9, 1951 N. E. DAVIS 2,570,650

HIGH-FREQUENCY WIDE BAND COUPLING TRANSFORMER Filed April 11, 1947 a sheets-sheet s R 7 Q 6 4 -i z. i

Patented Oct. 9, 1951 HIGH-FREQUENCY WIDE BAND COUPLING TRAN SFORMER Norman Eustace Davis, Chelmsford, England, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application April 11, 1947, Serial No. 740,830 In Great Britain March 4, 1946 9 Claims. 1

This invention relates to Wide band coupling transformers for use on very high frequencies.

Couplin transformers are often required, especially in television transmitters, for coupling high power amplifier circuits dealing with wide modulation band widths. In such arrangements it. is important to obtain a high and, if possible, substantially constant coupling coefiicient, but it is often very difiicult to achieve this since practical requirements frequently involve that there should be good physical clearance between primary and secondary circuits to give adequate protcetion against high operating voltages.

The present invention seeks to provide improved variable wide band coupling transformer arrangements suitable for use for coupling high power amplifier circuits in television transmitters although, of course, the invention is not specifically limited to this application. In a preferred embodiment of the invention, the transformer is made adjustable as to frequency.

According to this invention, a wide band coupling transformer suitable for use in a television transmitter or for like purposes consists in efiect of two coupled resonant line inductances and comprises two pairs of parallel conductors shortcircuited together at one. end and connected togather by a lumped capacity at the other, two shroud members each of approximately 0, openbox, or U-shape connecting together a conductor of. one pair with the corresponding conductor of the other so as to form two mechanical: structures, of they conductors, and. shroud members, and a coupling, coil between the two structures and passing. within the shroud members. Preferably at least one shroud-conductor structure is; made in two parts, one part arranged, to telescope an,- other, and means are provided for variably telescoping the two parts of said structure soas to vary the distance between. the conductors of one structure and the parallel conductors of the other. Preferably also, the conductors are tubular, the shroud members double walled, and the coupling coil isa. single turn coil.

The invention is illustrated in the, accompanying. drawings in which:

Fig. 1 is a simplified perspective, View of one embodiment;

Fig. 2 is a part side elevation view showing; the two structures of an alternate embodiment of a coupling transformer in accordance with, the invention;

Fig. 3 is a vertical section through; one such structure; and

Fig. 4. is a sectionalplan of the structureof Referring to Fig. 1 of the drawings, the transformer therein shown comprises two structures which are generally similar. Each such structure comprises two parallel metal tubes A, A1 connected together over their lengths by a double walled shroud member B of approximately rightangled U shape, the space between th walls of the shroud member being about two-thirds the tube diameter. The double walled parallel limbs B1, B2 of the U are fixed as shown on the one hand or telescopically arranged as shown on the other hand, and can be expanded or telescoped, preferably by means of nut and screw shaft arrangements housed within each limb, as shown in details with reference to a further embodiment of the invention.

The second structure may be exactly the same as the first but preferably the telescopic shroud arrangement with its operating shafts, gears and nuts is dispensed with, said second structure being of fixed dimensions. The tubes. of the second structure are parallel to the corresponding tubes of the first and lie in a. plane parallel to that containing the said tubes of the first structure so that, viewed endwise, the four tubes lies at the corners of an imaginary rectangle. A single turn tubular coupling coil G lying in a plane at right angles to the parallel planes of the tubes of the two structures provides coupling, a part (about-a quarter of a turn) of the coupling coil passing down between the limbs of the U of the one shroud member, and a similar partpassing down between the limbs of the U of the other shroud member. A flexible connector H provides the necessary short circuiting at one end of the resonant line which is shunted at the other (open) end by a lumped capacity C of suitable value where'C isthe shunt capacityacross the open-end of the line, I is the minimum length of the" line in centimeters, is the wavelength, and Z0 is the surge impedance in ohms, Z'being'less' than It. will be; seen from. the above equation that for a fixed end: capacity C and a. fixed line length l,

the maximum frequency varies inversely with Z0.

Now in a parallel wire or tubular line the parallel tubes or rods, and d is the diameter of each wire or tube.

It will be seen, therefore, that for a fixed diameter d, Z (and therefore ,1 max) may be varied by varying D, and this is the principle which is preferably adopted in carryin out the present invention to achieve a variable inductance coupling combination which results in a high and appreciably constant coupling coefficient throughout a range of frequency variation. Referring to Figs. 2-4, there is shown an alternate embodiment of the invention similar in structure to the basic arrangement shown in Fig. l. The principal feature of the alternate arrangement lies in the fixed construction of the shroud elements B with the tubes A and A1 adjustably positioned thereon. It will be seen that with the construction above described a good and substantially constant coupling coefiicient is obtained with safe physical spacing for good insulation against high voltage. In this embodiment tubes A, A and A1, A1 are drawn closer together or spaced farther apart as desired to vary the distance D therebetween in accordance with the desired frequency and constancy of coupling.

Tubes A and A1 are connected to the double walled parallel limbs Bl. and B2 of the U by means of a plurality of flexible contact members K. Furthermore, the spaces between the double walls at the bottoms of the Us are available for the housing and electrical screening of electron discharge tubes, or parts thereof, and in particular for the housing and electrical screening of water connections for water cooled electron discharge tubes such as often are employed in television transmitter amplifiers. In the arrangement illustrated in Fig. 2, discharge tubes are represented at J and water connections at W. Tubes A, A1 are telescopically arranged on limbs B1 and B2, and can be expanded ortelescoped by means of nut and screw shaft arrangement C housed within each limb Bi and B2, the shafts being driven together by bevel or other gears D by a manually or otherwise rotatably controlled shaft E housed within the double walled base of the U and having one end F projecting out of the housing for rotation purposes as shown in Figs. 3 and 4.

A transformer as above described with tubes 50 centimeters long and centimeters in diameter with a lumped capacity shunt of 50 micro-microfarads, gave (in experimental test) a frequency range of 40 to 65 mos. for a variation of D of 6 to 3 inches, with a constancy of couplin coefficient of within plus and minus 1 in 35.

What is claimed is:

l. A wide band coupling transformer consisting in effect of two coupled resonant line inductances and comprising two pairs of parallel 4 shroud members is utilized for the housing and electrical screening of at least parts of electron discharge tubes and for housing and electrical screenin of water connections for cooling said electron discharge tubes.

3. A wide band transformer consisting in effect of two coupled resonant line inductances and comprising two pairs of parallel conductors, means short-circuiting the conductors of each pair at one end, and a lumped capacity coupling together the conductors of each pair at the other end, two metallic shroud members connecting together a conductor of one pair and the corresponding conductor of the other so as to form two mechanical structures of the conductors and shroud members, at least one metallic shroud conductor structure being made in two parts, one part arranged to telescope the other, and means including a pair of beveled gears located within the metallic shroud member for variably telescoping the two parts of said structure so'as to vary the distance between the conductors of one structure and the parallel conductors of the other, and coupling means located adjacent said parallel conductors.

4. A wide band coupling transformer including two coupled resonant line inductors and comprising two pairs of parallel conductors, means shortcircuiting the conductors of each pair at one end, capacitors coupling together the conductors of each pair at the other end, two metallic shroud members each approximately U-shaped connecting together a conductor of one pair with the corresponding conductor of the other so as to form two mechanical structures of said conductors and said shroud members, a coupling coil arranged between the two structures and lying in a plane normal to the parallel planes of said conductors, a portion of said coil extending within one shroud member and another portion of said coil extending within the other shroud member, at least one metallic shroud conductor structure comprising two parts, one part arranged to telescope within the other, and means for variably telescoping the two parts of said structure to vary the distance between the parallel conductors of one structure and the parallel conductors of the other.

5. A wide band coupling transformer structure including a pair of resonant line inductors, each of the inductors of said pair of inductors comprising two tubular conductors, a capacitor connecting said tubular conductors at one end and a short circuiting element connecting said tubular conductors at the other end, said inductors being arranged adjacent each other in parallel relationship, said conductors being maintained in said arrangement by means of two shroud mem bers, each of said shroud members comprising two conductive sheet members of generally U-shaped cross section, one of said members arranged to nest within the other to form a generally U- shaped passageway therebetween, the edges of said conductive sheet members being connected to corresponding ones of said tubular conductors of said pairs of inductors.

6. A wide band coupling transformer structure including a pair of resonant lino inductors, each of the inductors of said pair of inductors comprising two tubular conductors, a capacitor connecting said tubular conductors at one end and a short circuiting element connecting said tubular conductors at the other end, said inductors be ing arranged adjacent each other in parallel relationship, said conductors being maintained in said arrangement by means of two shroud members, each of said shroud members comprising two conductive sheet members of generally U- shaped cross section, one of said members arranged to nest Within the other to form a generally U-shaped passageway therebetween, the edges of said conductive sheet members being connected to corresponding ones of said tubular conductors of said pairs of inductors, the spacing between the individual conductors of each of said inductors being adjustable.

7. A wide band coupling transformer structure including a pair of resonant line inductors, each of the inductors of said pair of inductors comprising two tubular conductors, a capacitor connecting said tubular conductors at one end and a short circuiting element connecting said tubular conductors at the other end, said inductors being arranged adjacent each other in parallel relationship, said conductors being mantained in said arrangement by means of two shroud members, each of said shroud members comprising two conductive sheet members of generally U- shaped cross section, one of said members arranged to nest within the other to form a generally U-shaped passageway therebetween, the edges of said conductive sheet members being connected to corresponding ones of said tubular conductors of said pairs of inductors, at least one of said shroud members being arranged in two parts, one part telescoping within the other to vary the spacing between the individual conductors of each of said inductors.

8. A wide band couplin transformer structure including a pair of resonant line inductors, each of the inductors of said pair of inductors comprising two tubular conductors, a capacitor connecting said tubular conductors at one end and a short circuiting element connecting said tubular conductors at the other end, said inductors being arranged adjacent each other in parallel relationship, said conductors being maintained in said arrangement by means of two shroud members, each of said shroud members comprising two conductive sheet members of generally U- shaped cross section, one of said members arranged to nest within the other to form a generally U-shaped passageway therebetween, the edges of said conductive sheet members being connected to corresponding ones of said tubular conductors of said pairs of inductors, the connection between the edges of said conductive sheet members and said conductors being made by flexible contact elements to permit variation of the spacing between the individual conductors of each pair of inductors.

9. A wide band coupling transformer including a coupling coil and two tubular conductive members having hollow U-shaped cross-sections arranged parallel to each other substantially to enclose said coupling coil, conductors interconnecting said conductive members at given ends thereof and capacitors interconnecting said members at the other ends thereof, at least one of said conductive members comprising at least two parts, one part arranged to slide within the other, and means for adjusting the two parts of said conductive member to vary the distance between said two hollow U-shaped conductive members.

NORMAN EUSTACE DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,342,896 Salzberg Feb. 29, 1944 2,395,441 Alford Feb. 26, 1946 

